Closed loop thermodynamic systems utilizing a vaporizable fluid, for the transfer of energy from an energy source to an energy utilizing means or for conversion of energy from thermal energy to mechanical energy, are well known. Such systems are particularly suited for solar energy conversion establishments in remote locations.
Typically, in a closed loop thermodynamic system of the type contemplated in relation to the present invention, a vaporizable working fluid undergoes a change of state from its liquid to its vapor form and back during a complete thermodynamic cycle. The system typically includes a boiler or other comparable element that receives thermal energy from an external energy source, e.g., the sun or a furnace, to vaporize the working fluid from its liquid to its vaporized state, energy utilizing means such as an engine connected to the boiler to receive the vaporized working fluid therefrom at a relatively high specific enthalpy, a condenser or the like that serves as a heat sink and condenses exhausted vaporized working fluid to its liquid state following its productive use in the heat utilizing means, and appropriate well known piping and means such as a pump to transfer the condensed working fluid back to the boiler with or without natural convection.
As persons skilled in the art must know, in such a closed loop thermodynamic system the Second Law of Thermodynamics requires that at least a portion of the energy received from the external energy source be rejected to a low temperature heat sink for the thermodynamic cycle to repeat itself. Such persons will also appreciate that the condensate formed in the condenser is at a relatively low pressure in the system and that cyclical operation of the system requires that the pressure of this liquid working fluid be raised to the working pressure of the boiler.
It is also well known in the thermodynamic arts that thermal regeneration, i.e., transfer to the condensate of some of the heat that must be surrendered by the system to the low temperature heat sink, prior to reentry of the condensate into the boiler, has the effect of increasing the thermodynamic efficiency of the system. This step of thermal regeneration is most effective, under most practical operating conditions, when the regenerative heat transfer causes energy to be added to the condensate after its pressure has been raised to essentially its highest value, e.g., soon after it exits from a flow pump if one is provided in the system.
Closed loop thermodynamic systems, particularly for solar energy conversion establishments, tend to operate at relatively low temperatures and may utilize liquids other than water as the working fluid. Fluids found to be relatively convenient for such uses include various freons and ammonia. Obviously, leakage of such a working fluid from the system can be both expensive and undesirable in that it would release a pollutant to the atmosphere. Pumps with excellent sealing are known and are readily available for use in such systems and, generally, require only periodic maintenance with controllable consequential interruption in the operation of the overall system.
An example of a pumpless system without regeneration, titled "Closed Loop Solar Collective System Powering a Self-Starting Uniflow Engine", U.S. Pat. No. 4,698,973, was issued to me on Oct. 13, 1987. It is incorporated herein by reference for its teaching of a closed loop thermodynamic system the efficiency of which can be improved by the provision of thermal regeneration. In this prior art system, the boiler element contains liquid working fluid approximately at a level at which two interconnected and cooperating working fluid holding tanks are located below a condenser element. A uniflow reciprocating vapor driven engine, preferably delivering useful mechanical output at a rotating shaft, is utilized as an exemplary "heat-utilizing" device in this known system.
Another patent, U.S. Pat. No. 4,805,410, issued to me on Feb. 21, 1989, titled "Closed Loop Recirculation System for a Working Fluid With Regeneration," teaches a pumpless system that provides the benefits of a regenerative system and, like my earlier cited patent, operates without a pump. Both these patents, U.S. Pat. Nos. 4,698,973 and 4,805,410, are incorporated herein by reference, especially for their teaching of the manner in which the working fluid recirculates in a closed loop without a pump.
There is, however, a need for a highly dependable and improved closed loop recirculation system in which the working fluid is provided with thermal regeneration, in which working fluid pressure differences are enhanced by a pump in the system which utilizes the boiler and condenser pressures and the force of gravity to the extent possible, and provides recirculation with thermal regeneration in a safe, reliable and efficient manner while effecting the necessary working fluid flows.